how can I import combinations

Hello,

Thank you for your post.

Combination ID's can not be used for identification while import. You may use the Combination references if you have ones.
In case you do not have a combination references, you can import combination without the identifier.
The Store Manager requires the identifier only products identifier. There is no need to use the combination identifier, as the Store Manager does not update the existing combinations and regenerates a new ones according to the records in the .csv file.

You can find more details on how to import product combinations in the article below:

http://www.prestashopmanager.com/useful-articles/tips-tricks/tips-on-how-to-import-prestashop-attributes